How do they know it opposes their position until they anayze it?
There are many different strategies. A very common one is to ignore evidence that even hints at being in opposition to their views.
But we've also seen lots that will avoid following certain lines of argument. They may well have seen them before so they know where they might go.
Jar is particularly good at flushing out this kind. He starts in very small steps; very simple facts that are hard to argue with and leads along step by step. Very frequently the creo he's talking to goes away or starts off into all sorts of tangents moving like a fly that has been swatted at. They will NOT allow themselves to go down certain paths.